116 Review of Dr. Thomson 



much from the latest determinations ; while those for soda and 

 potash are exact. 



Berzelius, familiar at an early period with Richter's specula- 

 tions, was naturally prepared to embrace Mr. Dalton's views of 

 atomic combination. He zealously set to work to determine, by 

 the most refined and rigid methods of analysis, and synthesis, the 

 true proportions in which chemical bodies combine. His success- 

 ful labours formed the ground- work of Dr. Wollaston's valuable 

 memoir on chemical equivalents. It is meanwhile worthy of re- 

 mark, that Berzelius should very rarely have had recourse to 

 Richter's method of mutual precipitation, in order to infer the 

 atomic number of an unascertained salt, or of its constituents, 

 from that of one already known. 



Dr. Thomson is the first chemist who has methodically pursued 

 this very simple and obvious route. Operating with the purer 

 salts of modern times, he has been enabled to rectify and define 

 the atomic numbers of a good many compounds ; and thence also 

 to deduce, on some occasions, the atomic weights of their consti- 

 tuents. He commenced this task in the " Annals of Philosophy, 

 for Nov. 1820," in which he published the atomic weights of ba- 

 rytes, potash, soda, muriatic acid, protoxide of lead, sulphuric, 

 nitric, and chromic acids. Of the numbers for the first four, as 

 stated by Dr. Wollaston, he corrected the second decimal figure ; 

 the others seem to have admitted of scarcely any alteration, for 

 Dr. Thomson's numbers nearly coincided with the previous deter- 

 minations of Wollaston and Berzelius. 



In verifying atomic numbers by the method of mutual saline 

 precipitation, had Dr. Thomson been careful to ascertain that the 

 decomposition was complete, as he might have done by suitable 

 re-agents, much more confidence might have been reposed in his 

 labours. But he has very frequently neglected this essential pre- 

 caution, as we shall shew in the course of this examination of his 

 work, and hence he has pretty often presented us with results, 

 tallying well with the atomic theory, and with Berzelius, which 

 he states as his own, though they could never have been derived 

 from his narrated experiments. He has been also somewhat im- 

 prudent in quitting the solid track of precipitation, and of trying 

 by novel methods, to demonstrate the truth of the idea suggested by 

 Dr. Prout, that the atomic weights of all chemical bodies are 

 multiples, by a whole number, of the atomic weight, of hydrogen. 



Ceratis ope Dcedalea 

 Nitilur pennis. 



The ingenious author of that proposition adduced so many exam- 

 ples, and analogies, as to render it highly interesting and plausible ; 

 and it has accordingly been regarded with a partial eye by the 

 most eminent of our chemical philosophers. The beautiful law 

 of gaseous combinations, discovered by M. Gay Lussac, and their 



